A senior US official has warned that a deal to save the nuclear accord with Iran is neither imminent nor inevitable as diplomatic efforts stall over Tehran’s demand that Washington removes a terrorist designation on the elite Revolutionary Guards.

Rob Malley, the US special envoy for Iran, said that a deal was “not just around the corner and is not inevitable”.

The Biden administration has been holding indirect talks, mediated by the EU, with Iran for 12 months in the hope of securing an agreement that would lead to Iran drastically reducing its nuclear activity. In return, the US would rejoin the accord and lift many sanctions on the Islamic republic.

Western and Iranian officials have for weeks been saying they are close to a deal. But Tehran insists the US meet its final demands, including delisting the Revolutionary Guards, the state’s most powerful military force, and providing guarantees that no future US administration is able to unilaterally abandon the deal.

“I can’t be confident it is imminent,” Malley told a conference in Doha. “A few months ago we thought we were pretty close as well. At any negotiation when there’s issues that remain open for so long, it tells you something about how hard it is to bridge the gap.’

The crisis with Iran was triggered by former US President Donald Trump’s decision to abandon the accord in 2018 and impose sanctions on the republic, including the designation on the guards. He also imposed sanctions on dozens of Iranian officials, including President Ebrahim Raisi, before he took power, and the office of Ayatollah Ali Khamenei, the supreme leader.

The guards train and arm proxies across the Middle East and are accused by western powers and their allies of stoking conflict and instability across the region. The force was under US sanctions before Trump designated it a terrorist organization.

If the Biden administration delisted the guards it would risk triggering a political backlash in the US and infuriating Washington’s partners in the

Middle East, including Israel, Saudi Arabia, and the United Arab Emirates.